When erecting building structures of reinforced concrete and especially such containing precast units, not only the characteristic load values in the service and ultimate limit states should be considered, but also special regard should be paid to accidental loading (explosion, impact from vehicles, fire, seismic action, settlements of foundations, etc.), such that progressive collapse will be prevented in case of a local failure in the structure. In this connection, the available ductile capacity of the connections between the various structural units is of great importance. If it is sufficiently large, alternative load bearing paths can develop when the structure is deformed, energy is absorbed from dynamic action and the falling down of structural units is prevented.
Connections between various structural parts can have many forms. Common for most of them is, however, that they contain ties (tie means) anchored in the facing structural parts, and generally made of steel and having the ability to transfer tensile forces. When the structural units are made of reinforced concrete, the ties normally extend a distance into the structural parts where they are anchored.
Current technology normally uses connections which, with regard to the circumstances in case of accidental loading, have a limited ductile capacity before rupture occurs in the ties. Their capacity to absorb energy in case of dynamic action is also limited. The available ductile capacity essentially depends on the yielding capacity, the length and the bond distribution along the tie devices when their ultimate tensile capacity is reached at the joint interface.
Limited arrangements to minimize the risk of progressive collapse are thus often regarded as satisfactory, or the risks are diminished in other ways than by dimensioning the connections utilizing their ductility.